Development of a new excavation technique for centrifuge testing in sand

Abstract

Even though shaft excavation is a key part of tunnelling projects in large cities, many uncertainties about their actual performance still exist in practice and only very few case studies have been reported in the literature. In this research work, centrifuge testing was used to investigate the performance of circular shafts and the adjacent ground movements during excavation. The most widely used excavation technique in centrifuge model-ling, employs a hydrostatic stress state which may not be the case in practice. This paper describes novel apparatus and centrifuge testing procedures that were developed to simulate shaft excavation in dry sand. The dry sand was carefully removed from the centre of a circular shaft under a centrifugal acceleration of up to 125 times the earth's gravity. The new in-flight excavation system allows more realistic stress changes to be induced on the shaft lining, compared with existing techniques. Detailed centrifuge test measurements of longitudinal bending and hoop strains in the circular shaft lining and displacement of the adjacent ground during excavation, reported in this paper, provide invaluable insights for future shaft construction.